This invention relates generally to the art of blow molded containers and the molding thereof and more particularly to the art of forming a single-walled blow molded container having an integral hinge portion.
Single-walled thermoplastic containers have been produced in the prior art by utilizing injection molding techniques. Molds for injection molding processes are considerably more expensive and complex than molds utilized for blow molding since a mold surface is required for every surface of the resulting injection molded article. An example of such prior art injection molding is described in U.S. Pat. No. 2,687,157 to Cowan.
U.S. Pat. No. 3,795,265 to Schurman et al describes a process of producing a double-walled container having an integral hinge. In an aspect of the invention disclosed therein, there is provided a container having a body part and a cover part joined by a hinge continuous with each of them and connecting them for opening and closing the container. The body part, cover part and hinge are formed from a single plastic tubular member. The hinge is a pressed and fused laminate of two webs formed from opposite sides of the tubular member. The hinge is thinner than the adjacent wall area of the body part and the cover part, as a result of the pressing and the pinching of the hinge during its formation.
The method described by Schurman et al involves the use of an unrestrained parison and a mold having male mold parts that make a substantial entry into the mating female mold parts. The method includes extruding the parison, positioning the unrestrained parison in the mold, closing the mold on the parison until the male mold parts project substantially into the mating female mold parts deforming the parison between them into the general configuration of the finished molded parts and inserting a blow needle through the wall of the parison and expanding the parison by providing a pressure differential between the inside and the outside of the parison by blowing a pressurized fluid into the interior of the parison thus forcing the parison into the detailed configuration of the closed mold.
The two mold cavities are joined by land surfaces that register in closely spaced opposed relation when the mold is closed. The parison is closed at opposite ends and pinched upon itself intermediate its ends, upon the closing of the mold, and compression molded at its intermediate pinched area between the land surfaces to form a hinge separating the parison into a pair of hollow compartments.
While the product described in the above-referenced United States patent provides an excellent double-walled container with an integral hinge, it is not always necessary for a container to have the double-wall construction described therein.